Scout,

He can't be at the starting point and be asking the name of the Vector
between the start and where he finished. Logical?

Also, even if there was no deviation due to Tidal drift, leeway etc,
just sail by "Timed Legs" on globe cannot make a square anywhere except
equal distance north & south of the equator or at the north or south
poles.

Scout, even if you sail a straight course you are sailing a curved line,
as far as elevation is concerned. This in itself will cause a course
change from East to South to be something different than a square corner
of a box.

Think of an ice cream cone, with the pointy end being north. Draw a
straight line from the lip of the cone to the tip (North) Now rotate the
cone 90 degrees and draw another line to the tip (North again) Now Scout
draw a line parallel to the lip of the cone, between those two lines. Is
it a square? Is it the same distance as the of the lip? It isn't is it?
Make it the same distance. Now, can you connect the ends with two
north---south lines to make a square?

I hope this help rather than confuse but I hope it helps explains the
problems of compass headings and expanding degree on a globe. It is a
concept worth getting a handle on.

Ole Thom